Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
The problem of infertility in cattle is one that the veterinary profession is far from solving. Research on the problem has been intensified during the last 10 years, but as yet the basic factors involved in the problem of the repeat breeding cow are still puzzling or unknown. Heredity may rarely play a part, but it does not explain the average infertile cow.
Gibbons, W. J.
"The Treatment of Infertility in Cattle,"
Iowa State University Veterinarian: Vol. 20
, Article 2.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol20/iss2/2